WASHINGTON—For the past several months, Mitt Romney has been the inevitable nominee — ahead in national and early state polls — and he's acted like it, with an almost-singular focus on President Barack Obama.

That all changes tomorrow.

For the first time the Romney campaign is going after one of his party's own: Newt Gingrich, the new Republican front-runner whose commanding leads in Iowa, South Carolina, and Florida have Romney rethinking his strategy.

Former New Hampshire Governor John Sununu and former Missouri Senator Jim Talent will hold a press conference call tomorrow morning "to discuss Speaker Newt Gingrich’s record," according to the campaign. Historically these venues have previously been used by Romney almost exclusively for Obama attacks — with no less than ten calls in a single day last month going after the White House.

If Gingrich collapses tomorrow, he has succeeded at doing what the other boom-and-bust GOP candidates have failed at — drawing Romney out into sustained attack mode. Romney and Perry notably traded barbs at some early debates, but it was never serious; and the rest of the Romney campaign remained focused on Obama.

Romney has spent the past six months hiding from the media and reluctant to make waves, preferring to allow the rest of the field to rise and fall around him. But with his once-stable 23 percent in the polls eroding, Romney now has no choice but to act like a candidate, and not the nominee.

Gingrich's lead at the top of the polls is nearing the end of its second week — with no sign of letting up — Romney's has little choice but to go on the offensive.

Tomorrow's call will no doubt be more substantive, but the risk Romney runs by attacking Gingrich is that he's vulnerable to many of the same charges he can level against the former Speaker of the House. Both have inconsistencies in their records, and Romney will have to take care to avoid his attack backfiring — while at the same time moving as fast as possible to deflate the air from the Gingrich bubble before it solidifies.

With less than four weeks to the Iowa Caucuses, Romney's running out of time.